Piston drive mechanism



March 8, 1966 v, J, HUBER ETAL 3,238,889

PISTON DRIVE MECHANISM Filed June 5, 1963 2 Sheets-Sheet 1 -44 A Z] 23Z6 22 Z6 Z0 25 f1 24 27 I 49 L 5'4 55 47 f9 4/ 5 INVENTOR 1 /6, 3VNVCF/VT J #0551;

JAMES 5. Mc CART/V5) ATTORNEY March 8, 1966 v. J. HUBER ETAL 3,238,889

PISTON DRIVE MECHANISM Filed June 5, 1963 2 Sheets-Sheet 2 34 l v 55INVENTOR 44 V/A/CE/I/T d. //(/BR I I JAMES 5. Mc (ARM/fr 3/ W BY g w gATTORNEY United States Patent 3,238,889 PISTON DRIVE MECHANISM VincentJ. Huber, Shakopee, and James S. McCartney, St. Paul, Minn., assignorsto Aero Spray Inc., Minneapolis, Minn., a corporation of Minnesota FiledJune 3, 1963, Ser. No. 285,125 10 Claims. (Cl. 103-171) This inventionrelates to an improvement in piston drive mechanisms and dealsparticularly with a means of driving a reciprocable piston in such amanner that it will rotate about its axis as it is reciprocated.

Various types of piston mechanisms have been provided which arereciprocated by an eccentric mounted on a shaft having its axisintersecting the axis of the piston at right angles. Such pistons areusually provided with a piston rod of smaller diameter than the pistonand including parallel shoulders which are spaced apart a distancesubstantially equal to the diameter of the eccentric roller or hearing.For example, compressors and vacuum pumps have been produced comprisingan elongated cylinder having a pair of connected pistons reciprocabletherein. The pistons are reciprocated in unison by an eccentric rolleror hearing supported eccentrically upon a drive shaft, the axis of whichintersects the axes of the pistons. During one hundred eighty degrees ofrotation of the drive shaft, the pistons are urged in one direction, andduring the remaining one hundred eighty degrees travel of the driveshaft, the pistons are moved in the opposite direction. Means areprovided for admitting air into the cylinder ends during movement of thepistons away from the end, and permitting air to escape from thecylinder end during the compression stroke.

One of the difficulties which has been experienced with devices of thistype lies in the fact that the eccentric roller or hearing engages thesame areas of the pistons ends or abutments against which the eccentricroller engages, causing undue wear in this area. Furthermore, in theevent any abrasive material enters the cylinder, this material may enterthe small clearance between the pistonand the cylinder and be movedlongitudinally of the cylinder as the piston reciprocates, providinglongitudinal groove in the wall of the cylinder, of the piston, or ofboth. In actual practice, some structures of this type have beenactually worn out after a relatively few hours of continuous operation.

We have found that the life of a piston structure of this general typecan be prolonged many times its normal life if the piston structure isrotated about its axis as it reciprocates. As the piston structurerotates about its axis, the eccentric cam or bearing continually engagesa different point on the abutments against which the hearing engages.Furthermore, any abrasive particles which are accidentally entrappedbetween the piston structure and the wall of the cylinder alsocontinually engage a different portion of the surface of the pistonstructure and cylinder, so that the tendency of such a particle to weara longitudinal groove is eliminated.

We have found that by making the surface of the abutment on one side ofthe eccentric roller or hearing concave, and making the surface of theother abutments slightly convex, the piston structure will automaticallyrotate about its axis as it is reciprocated. It is believed that this isdue tothe fact that as the substantially cylindrical surface of theeccentric roller is forced against the concave surface of the abutment,the edge of the eccentric roller which is farthest from the axis of thepiston shaft bears against this surface in a manner to create a momentarm tending to rotate the piston structure in one direction about itsaxis, while when the cam roller exerts its force in the oppositedirection, the edge of the eccentric roller which is nearest the axis ofthe piston structure exerts a force tending to rotate the pistonstructure in an opposite direction. However, due to the fact that themoment arm is considerably reduced when the eccentric roller engages theconvex surface, an unbalanced force is created, and the rotation of thepiston caused by the engagement of the eccentric roller with the concavesurface overrides the tendency of the piston to rotate in the oppositedirection.

A further feature of the present invention resides in the fact that asomewhat similar result may be accomplished by arranging the axes of thepiston and the drive shaft on a common plane with the axes thereofintersecting, but in locating the axis of the drive shaft of slightlymore or less than ninety degrees from the axis of the piston. However,better results have been produced by having the surfaces of theabutments of frusto-conical form, one surface being slightly concave andthe other surface being slightly convex.

These and other objects and novel features of the present invention willbe more fully and clearly set forth in the following specification andclaims.

In the drawings forming a part of the specification:

FIGURE 1 is a longitudinal sectional view through a double actingcompressor or vacuum pump showing the general arrangement of partstherein.

FIGURE 2 is an elevational view of the piston used in the pump, theconcavity and convexity of the piston ends being materially exaggeratedto show the principle.

FIGURE 3 is a view similar to FIGURE 2 showing the piston structure atone end of its stroke.

FIGURE 4 is a transverse sectional view through the compressor, theposition of the section being indicated by the line 4-4 of FIGURE 1.

FIGURE 5 is a transverse section on the line 55 of FIGURE 3.

FIGURE 6 is an enlarged view of a portion of the piston drive mechanism.

To simplify the description, the apparatus will be described as acompressor. However, by changing the arrangement of the ports, the samedevice can be used as a vacuum pump. The present structure has beenfound particularly advantageous in this type of device, but it should beunderstood that the same drive principle could be used in other types ofpiston structures where the piston is reciprocated by an eccentricroller or hearing movable between two abutments on a shaft coaxial withthe piston.

The compressor A includes an elongated cylinder 10 which is intersectedintermediate its ends with a transverse bore 11 extending through a pairof right angularly extending bosses 13 and 14. The boss 13 is providedwith a peripheral flange 15 through which angularly spaced bolts such as16 may extend to secure the housing 17, including the cylinder 10 andbosses 13 and 14 to a motor 19. The motor 19 is provided with a driveshaft 20 which projects into the bore 12, preferably in coaxial relationthereto.

In the particular arrangement illustrated, the end portions of thecylinder 10 are counter bored to a larger diameter than the centralportion of the cylinder as indicated at 21 and 22. Mounting rings 23 and24 are provided in the counter bores 21 and 22 and support rings 24 madeof low friction material such as resilient plastic materialpolytetrafiuoroethylene known to the trade under the trademark Teflonalso in the particular arrangement illustrated, the mounting sleeves 21and 22 may support spacer rings 26 and 27 respectively which hold theTeflon rings 24 and 25, as well as the angular wiper rings 2% and 30 inposition.

The rings 24 and and wiper rings 29 and 30 slidably support a doubleended piston unit including a pair of pistons 31 and 32 connected by aconnecting rod 33 which is coaxial with the pistons. In the arrangementillustrated, the inner opposed ends of the pistons 31 form the abutmentsagainst which the drive roller engages. The piston 31 is provided with afrusto-conical concave surface 34 while the piston 32 is provided with afrustoconical convex surface 35. The concave surface 34 is at an angle36 to a plane normal to the axis of the pistons, while the convexfrusto-conical surface 35 of the piston 32 is at an angle 37 to a planenormal to the axes of the pistons. The angles 36 and 37 are equal andare shown in greatly exaggerated form in FIGURE 2. In the structuresproduced, are about one or two degrees. This angle has proven sufficientto create rotation of the pistons about their axes as they arereciprocated. In structures of different dimensions, this angle may haveto be increased or decreased.

As indicated in FIGURE 4 of the drawings, a sleeve 39 is secured to themotor shaft 20 to rotate in unison therewith, and this sleeve supports apivot pin 40 which is arranged with its axis offset from the axis of thesleeve. As indicated in FIGURE 3 of the drawings, the pivot shaft orstud 40 supports a ball bearing 41 having an inner race 42 and an outerrace 43. The diameter of the outer race 43 is approximately equal to thedistance between the abutment surfaces 34 and 35, the bearing fittingbetween the surfaces so that it will only contact one of the surfaces ata time, but so that there is no particular Waste space. As a result, asthe motor drive shaft 20 rotates in a clockwise direction as viewed inFIGURES 1 and 3 of the drawings, the bearing 41 will engage the concavepiston surface 34 as the piston structure moves to the left, and willengage the convex piston 35 as the motor shaft completes eachrevolution. As indicated in the greatly enlarged section of FIGURE 6,when the pistons are moving to the left, the outer race 43 of thehearing 41 engages an area 44 of the concave surface 34 of the piston 31which is located relatively far away from the axis of the pistons, thisaxis being represented by the broken line 45 in FIGURE 6. At the sametime, during the movement of the piston structure to the right as viewedin this figure, the bearing race 43 will engage the convex surface 35along an area 46 which is materially closer to the axis 45.

The ends of the cylinder are closed by end plates 47, and manifoldplates 49 abut against the end plates 47. The manifold plates 49 areprovided with a pair of generally semi-cylindrical recesses 50 and 51separated by a partition 52. The chambers 50 are connected by suitablepassages 53 to an air inlet 54, and these chambers 50 communicate withthe interior of the cylinder through passages 55. Check valves 56 permitair to enter the end of a cylinder from which the piston is moving.

The chambers 51 are connected by passages 57 to the outlet 59, and thesechambers 51 also communicate with the interior of the cylinder 10through ports 60. Check valves 61 close the ports 60 when the pistonsare moving away from the cylinder end, and open as the piston moves onits compression stroke to force air through the outlet 59.

The operation of the device as a compression pump or as a vacuum pump isbelieved obvious from the foregoing description. During thereciprocation of the piston unit, air is drawn into the end of thecylinder away from which the piston unit is moving, and air is forcedfrom the end of the cylinder toward which the piston unit is moving.

Insofar as the operation of the means of rotating the piston isconcerned, it is extremely difiicult to state with complete accuracyjust what takes place. However, it is noted that where the outer race 43of the bearing such as 41 operates between a pair of abutments which arenormal to the axis of the pistons, there seems to be some tendency forthe piston to rotate about its axis in one direction as the piston isbeing moved in one direction,

and to rotate in the opposite direction as the piston moves in theopposite direction. However, the forces against the two abutments areapproximately the same, and as a result no rotation of the piston unittakes place. It should be remembered that when the pump is in operation,the piston unit may reciprocate at a relatively high speed so that thetwo tendencies are equalized.

It is theorized that when the bearing engages the concave surface 34 ofthe piston 31, it engages the surface along the area 44 which is at aconsiderable distance from the piston axis 45. During the return strokeof the piston unit, the hearing or roller 41 engages the convex surface35 along the area 46 which is materially closer to the piston axis 45.As a result, the force tending to rotate the pistons about their axes inone direction greatly exceeds the tendency to rotate the pistons in theopposite direction, and the piston unit maintains a constant rotation.

Whether or not this theory of operation is a complete explanation of theoperation or not is not known. When the piston unit acts as a compressoror a vacuum pump, the pressures involved within the cylinder increasevery materially as the piston moves along its compression stroke. Thismight have some effect on the operation, when combined with the factthat the point of engagement between the eccentric roller and thefrusto-conical surfaces varies in radius from the piston axis as theeccentric rotates. It is known that the speed of rotation of the pistonassembly about its axis increases as the load against which the pistonassembly increases. This fact is also important, as when the apparatusis not operating under a load, the need for rotating the pistondecreases. In any event, it is known that as the piston reciprocates, italso rotates about its axis where the abutments are frusto-conical andformed in the manner described. Thus it is known that the structurebeing described and claimed accomplishes the desired result.

Some advantageous results have also been accomplished by locating theaxis of the motor shaft 20 on a plane with the axis of the pistons 31and 32 and wherein the axis of the motor shaft is slightly out of rightangular relation to the piston axes. When this is done, and when thefaces of the abutments are parallel and normal to the axes of thepistons, the edge of the outer bearing race most remote from the pistonaxis will engage one abutment during the movement of the piston unit inone direction, and a portion of the bearing which is relatively closerto the piston axes would engage the other abutment during the returnstroke. This arrangement does not appear to function as well as thepreferred structure, described, but the fact that it functions seems tobear out the applicants description of the operation.

If means are provided for carrying the eccentric past dead centerposition, the apparatus may also operate in reverse. If fluid isalternately directed to opposite ends of the cylinder 10, the pistonassembly may function to rotate the eccentric in its orbital path. Theshaft 20 could be provided with a flywheel, or two angularly arrangedpistons could be connected by the shaft 20, each serving to move theeccentric of the other unit past dead center position. In such an event,the piston assemblies would still rotate about their axes uponreciprocation.

In accordance with the patent statutes, we have described the principlesof construction and operation of our improvement in piston drivemechanisms, and while we have endeavored to set forth the bestembodiment thereof, we desire to have it understood that changes may bemade within the scope of the following claims without departing from thespirit of our invention.

We claim:

1. A piston drive means for use in reciprocating a piston assembly andsimultaneously rotating the assembly about its axis and including apiston assembly, a piston rod on said piston assembly and coaxial withrespect thereto, means providing a pair of shoulder abutments on saidpiston rod, a drive shaft means supporting said drive shaft with itsaxis intersecting the axis of said piston assembly, a rollereccentrically supported by said drive shaft to move in an orbital pathupon rotation of said piston said roller having a generally cylindricalouter surface, the cylindrical surface being somewhat inclined, relativeto the surfaces of said abutments so that the edge of the cylindricalsurface most remote from the axis of the piston assembly engages oneabutment and the edge of the cylindrical surface closest to the pistonassembly axis engages the other abutment when the piston assembly movesin the opposite direction the distance between the abutments beingslightly in excess of the outer diameter of said roller, and a cylinderslidably supporting said piston assembly.

2. The structure of claim 1 and in which the axis of said drive shaftintersects the axis of the piston assembly at right angles, and in whichsaid abutments are frustoconical, one abutment being concave and theother convex the two surfaces being parallel.

3. The structure of claim 1 and in which said piston assembly includes apair of pistons connected by a coaxial connecting rod.

4. The structure of claim 3 and in which the inner opposed ends of thepistons form the said abutments.

5. A piston drive means for use in reciprocating a piston assemblyaxially within a cylinder and simultaneously rotating said pistonassembly about its axis, including a piston rod on said piston assemblyand coaxial with respect thereto, means providing a pair of spacedparallel shoulders encircling said rod, a shaft rotatably supported onan axis intersecting the axis of said piston assembly and atsubstantially ninety degrees thereto, a roller supported by said shafton an axis parallel to said shaft axis and eccentric with respectthereto, said roller being supported between said shoulders andengageable therewith to reciprocate said piston assembly upon rotationof said shaft, one said shoulder having a frustoconical slightly concavesurface, the engagement of said roller with said surfaces acting torotate said piston assembly about its axis as it reciprocates.

6. The structure of claim 1 and in which said surfaces are at an angleof about one degree from a plane normal to the piston assembly axis.

7. A piston drive means for use in reciprocating a piston assemblyaxially within a cylinder and simultaneously rotating said pistonassembly about its axis, including a piston rod on said piston assemblyand coaxial with respect thereto, means providing a pair of spacedparallel shoulders encircling said rod, a shaft rotatably supported onan axis intersecting the axis of said piston assembly, said shaft andpiston assembly axes being in a common plane and at an angle of aboutone degree less than ninety degrees apart, a roller supported by saidshaft on an axis parallel to said shaft axis and eccentric with respectthereto, said roller being supported between said shoulders andengageable therewith to reciprocate said piston assembly upon rotationof said shaft the angular relation between the axes of said shaft andsaid piston assembly imparting a rotative force to said piston assemblyupon rotation of said shaft.

8. An apparatus including a housing having an aligned cylinder chamberat each end, a piston assembly in said housing including a piston ineach chamber and a connecting rod of smaller transverse dimension thanthe diameter of the piston connecting said pistons and drive means foraxially reciprocating said pistons and coopera'ble surfaces on saiddrive means and the inner opposed ends of said pistons for rotating saidpiston assembly about its axis,

9. A pump unit including a cylinder, a piston unit reciprocably slidablein said cylinder, said piston unit including a pair of spaced pistonsand a connecting member of reduced diameter connecting said pistons formoving the same in unison, piston reciprocating means including arotatable shaft having its axis intersecting the axis of said pistonunit and at substantially ninety degrees thereto, a roller supported bysaid shaft on an axis parallel to said shaft axis and eccentric withrespect thereto, means on said piston unit defining spaced parallelshoulders between which said roller is supported, one said opposedshoulder having a frusto-conical concave surface, and the other saidshoulder having a frusto-conical convex surface, and valved passagescommunicating with the ends of said cylinder to control the flow offluid to and from said cylinder ends.

10. A drive mechanism for use in rotating a piston as it reciprocatesincluding a cylinder, a piston assembly slidable axially of saidcylinder, a piston rod connected to said piston assembly and coaxialtherewith, a shaft arranged with its axis intersecting the piston axis,means providing a pair of spaced abutments on said rod and encirclingthe same, an eccentric roller mounted on said shaft on an axis parallelto and spaced from, the shaft axis, the diameter of said roller beingsubstantially equal to the distance between said spaced abutments, saidroller having a generally cylindrical outer surface, said surface beingsomewhat inclined relative to the surfaces of said abutments so that theedge of said roller most distant from said piston axis engages oneabutment as the piston assembly moves in one direction and the edge ofsaid roller nearest said piston axis engages the other said abutmentupon movement of said piston assembly in the opposite direction.

References Cited by the Examiner UNITED STATES PATENTS 2,354,980 8/1944Arras 74-50 X 3,021,716 2/1962 Goyette et a1. 74-50 FOREIGN PATENTS334,580 3/1921 Germany.

BROUGHTON G. DURHAM, Primary Examiner.

8. AN APPARATUS INCLUDING A HOUSING HAVING AN ALIGNED CYLINDER CHAMBERAT EACH END, A PISTON ASSEMBLY IN SAID HOUSING INCLUDING A PISTON INEACH CHAMBER AND A CONNECTING ROD OF SMALLER TRANSVERSE DIMENSION THANTHE DIAMETER OF THE PISTON CONNECTING SAID PISTONS AND DRIVE MEANS FORAXIALLY RECIPROCATING SAID PISTONS AND COOPERABLE SURFACES ON SAID DRIVEMEANS AND THE INNER OPPOSED ENDS OF SAID PISTONS FOR ROTATING SAIDPISTON ASSEMBLY ABOUT ITS AXIS.